1. Field of the Invention
The present invention relates to a CDM (Code Division Multiplex) receiver apparatus in a communication or broadcasting system using a CDM method, and a RAKE synthesizer apparatus used for the CDM receiver apparatus.
2. Description of the Related Art
In a CDM transmitter and a CDM receiver apparatus in a communication or broadcasting system using a CDM method, the following operations are usually performed. A CDM transmitter adds an error correction code to each transmission data of a plurality of channels, generates a CDM signal by spreading the data by a spreading code different for each channel and multiplying the data, and sends out the CDM signal. A CDM receiver apparatus performs AGC (Auto Gain Control) for the received CDM signal depending on the average receiving power, and then despreading demodulates the signal by using a spreading code of the specified channel, makes soft decision and corrects an error to thereby obtain the transmission data of a specified channel. A CDM receiver apparatus usually uses a RAKE synthesizer apparatus as a back diffusion demodulator.
However, in a despreading demodulator used in a conventional CDM receiver apparatus, the average amplitude (power) of output data does not always match the power level of input signal because of the influence of spreading and demodulating the signal by using the spreading code. Thus, even if the input power level of the despreading demodulator by performing AGC based on the average receiving power, the average amplitude of demodulated data is not fixed. As a result, the accuracy of soft decision lowers, and the error rate rises.